Ab-initio prediction of pressure-induced superconductivity in potassium

We report first principles calculations of the superconducting properties of fcc potassium under high pres- sure. Using a completely ab initio method we predict a superconducting phase transition at 18 GPa. A maxi- mum critical temperature of about 2 K is observed around 23 GPa, the pressure at which the crossover between the fcc phase and the KIII structure experimentally occurs. At higher pressure, when the fcc phase is experi- mentally unstable, we find, in the phononically stable range, values of T c up to 11 K. In order to understand the underlying mechanisms inducing superconductivity in potassium, we study the effect of pressure on the electronic and vibrational properties, showing a progressive phonon softening near the K point of the Brillouin zone and a concomitant enhancement of the electron-phonon coupling constant ␭. Interestingly, we find that the pressure induced s-d charge transfer causes an increasing anisotropy of the superconducting gap ⌬. Al- though similar to dense Li in many respects, K displays interesting peculiar features.